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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

Posted on 17 February 2012 by Glenn Tamblyn

In my under-graduate days, studying engineering some years ago (quite a few actually but the less said about that the better), one idea was drummed into us again and again. If you want to study any sort of system you absolutely need to define your ‘system boundaries’ correctly. What are the boundaries of the thing you are studying? Get this right and your analysis may be solid. Get it wrong and your analysis will be rubbish.

Bounding Around

So when we think about Global Warming we need to be really certain that our ‘system boundaries’ are right. So what is the theory of Global Warming, in a nutshell? And what does this tell us about where we need to set our boundaries. Put at its simplest, Global Warming says that more GH Gases will cause an imbalance between the amount of energy the Earth receives from the Sun, and the energy it looses to Space. More of the GH gases make it harder for the Earth to loose energy to space, so heat starts to build-up here. And this heat build up can lead to higher temperatures.

So what does this tell us about what needs to be inside our ‘system boundary’?

Our system boundary needs to include anywhere where this extra heat can accumulate! To understand Global Warming we need to look at all the places where heat can go and account for all of them.

And this is what the scientists have done. This graph, taken from the IPCC’s 2007 report shows the estimates of how much heat has been added to different parts of the environment – melting ice, warming the land, air and oceans between 1961-2003 and 1993 - 2003.

I have highlighted the atmosphere part for a very simple reason. This is what most of us think of when we talk about ‘Global Warming’; that it is changes in the air temperature!

Yet look at the graph; warming of the atmosphere really is small potatoes! The main game in Global Warming is what happens in the Oceans. Around 90% of the heat added since 1961 has happened there. In contrast warming of the atmosphere is only around 3% of the heat.

Here is a different way of looking at the same thing with data from Church et al 2011

So if we were to set our ‘system boundary’ incorrectly and just looked at the atmosphere, we would be looking at only a very small part of the system and could easily reach a poor conclusion. Like trying to understand the Dog by just looking at its Tail!

Pin the Tail on the …

So what has been happening in the oceans? How do we measure the data needed to produce these graphs? To understand this we need to measure temperatures down through the depths of the ocean at many points. Then by observing how these measurements change and knowing the thermal properties of sea water, its Specific Heat, we can start to calculate heat accumulation.

First a little bit of history. The very first measurements of deep ocean temperatures were performed with instruments lowered from a ship down into the ocean. This method is still used today for detailed studies and for looking at what is happening all the way to the sea bottom. But this method has a big disadvantage. A research ship is needed that can stop, lower a sensor platform over the side from a crane, and sample all the way down. This might take several hours to take measurements at one location. Then it moves on to another location. It is very slow and very expensive and doesn't actually cover much area.

In the 1960’s a better idea was developed. The Expendable Bathythermograph or XBT. A fairly simple, expendable device that could be dropped over the side of a ship while it was underway and report basic data as it sank. Then it just fell to the sea floor. And this didn’t just have to be done from research ships. Any commercial vessel could do it. So now there was a tool for gathering ocean temperature data cheaply from around the world. But it was limited to reporting the top 700 metres of the ocean.

Then through the 2000’s, a consortium of many nations began deploying a smarter answer; the Argo Float Array. This is a series of several thousand free floating ‘smart’ buoys that drift with the currents around the world’s oceans.

These buoys are able to auto-dive down to 2000 metres, measuring as they go, then surface and report their data, and their location via GPS, to satellites that collect the information. Now we have a more sophisticated measuring system for the world’s oceans. So what does all this data show us?

As the figure above suggests, most of the heat has gone into the oceans. But for the last decade or so Mother Nature has been playing some tricks!

Compare these two graphs which are from the National Oceanographic Data Centre (NODC) which also provides a range of other graphs looking at different aspects of sea level rise.

The upper graph shows data from the top 700 metres of the ocean. This is a combination of XBT data going back to the 1960’s and ARGO data. The second graph is showing data all the way down to 2000 metres. How can we have data to 2000 metres for those past decades when ARGO only began operation in the 2000’s? By combining data from 0-700 metres from the XBT’s, with deep data from the ‘lower a sensor over the side’ type measurement programs an estimate can be made of what was happening down deeper. But during the 2000’s we have live data from both depth ranges.

And the picture is rather strange! Up until the early 2000’s, the two trends are broadly similar. The top layer grew by about 1.7 x 1023 joules while the entire 0-2000 range warmed by about 2.1 x 1023 joules. The top layer contained about 80% of the added heat.

But for the last decade or so the top layer has nearly flat lined while the full range has continued warming. Since 2004 there is around 0.5 x 1023 joules in the full depth that isn’t in the top layer! It must be down deeper, between 700 & 2000 metres. What is Mother Nature up to? How can the deeper water be warming if the upper layer isn’t?

We pause briefly…

Here both Climate Models and Oceanography can come to our rescue. In a paper published last year Meehl et al (2011) looked at what a range of different climate models predict might happen in the future. And one rather surprising result they found were ‘Hiatus periods’. Periods of a decade or so where air temperatures - that 3% part that we live in - seem to plateau. But it is what the various models show is happening in the oceans during these periods that is really interesting.

During ‘normal’ periods, more heat goes into the upper part of the oceans and less into the lower depths. But during the ‘Hiatus’ periods, the top of the ocean doesn’t accumulate nearly as much heat whereas the next lower levels accumulate more. Exactly what the current ocean data is telling us!

But why? How can heat reach these greater depths without also heating the top layer?

It’s all about circulation patterns in the ocean. The major circulation patterns are about large surface and bottom currents. Connecting these are regions of major up-welling and down-welling – locations where significant exchanges occur between the surface and the abyssal deeps. But these abyssal deeps aren’t at 2000 metres – more like 5,000 to 8,000 metres.

However, there are also regions in the open ocean with smaller scale vertical-mixing currents that combine the very surface layer with the next level down.

Here for example is the climate model simulation of the mixing currents that overturn the upper layers of the ocean across the Pacific.

So all that Mother Nature has to do is crank these upper ocean circulation patterns up a notch for a period and heat is drawn down from the surface to the next level, to be replaced with colder water from below.

So lets consider what such a pattern will do to the Earth’s climate patterns while it lasts. The next lower level of the ocean will warm because warm water is being pumped down from above. The surface of the ocean won’t warm as much, if at all, because its heat is continually being pumped lower to be replaced by colder water. And because the ocean surface doesn’t warm very much during this period, the atmosphere doesn’t warm as much either. So from our rather limited perspective here on the surface it looks like warming has stopped. When in fact it is simply going on somewhere else. The Dog may have temporarily stopped wagging its Tail but the Dog is still trotting along.

And the models predict that these Hiatus periods last for a decade or so. Then the ocean heat patterns revert to their ‘normal’ structure. And the top layer of the ocean resumes normal heating. And then the Atmosphere resumes heating! So the Dog will resume wagging its Tail soon. It’s a Dog, it can’t help doing that.

So when you hear or read anywhere or are told by anyone that ‘warming stopped in (insertpreferreddate)’ the simple, observed fact is that it hasn’t stopped warming! It’s just that much of the warming has been happening somewhere else recently.

So anyone who says otherwise is simply falling into the most basic trap that any under-graduate engineer or scientist is taught to avoid. Not using the correct system boundary! And if the person saying this is a professional scientist or engineer what conclusion can we draw from their opinion? That they are incompetent? Or…?

The Smoking Gun

When the first studies of the XBT data were produced in then early 2000’s, showing just how much heat had been added to the oceans, the climate science community labelled this ‘The Smoking Gun’. They knew that increased Greenhouse Gases had to be causing a heat accumulation – the understanding of the physics of this is very solid. But they knew also that the Surface Temperature records that had been compiled to date only showed where a small percentage of the extra heat was going. The surface was warming much as the climate modelling predicted but until they could begin to confirm what was happening in the oceans, they didn’t have enough of the pieces of the jigsaw puzzle. They knew how to draw their system boundaries.

The appearance of the first studies on Ocean Heat Content during the 2000’s would have been one of the significant factors in the IPCC increasing its level of confidence that AGW was real in its 4th report in 2007.

Because the pattern of where the heat is going says something very important about what is causing it. It is sometimes argued that the global warming we are observing is due to internal variability, a recovery from the Little Ice Age etc. These suggestions are always based on just the surface temperature record. For these ideas to be reasonable, heat has to come from some other part of the climate system in order to warm the atmosphere. If every other part of the climate system is also warming at the same time then this cannot be ‘internal variability’. And if the total heat in the system is accumulating this can’t be due to a ‘recovery’ from the Little Ice Age. This must be new heat being added today.

But the absolute clincher is that the amount of heat going into the oceans is so great that no other source of heat here on Earth could supply it. The first two graphs at the start of this post are absolute proof that something is disturbing the Earth’s external energy balance. And since we know that the Sun’s energy output has, if anything, been declining slightly over the last ½ century the only remaining possibility is something affecting the Earth’s ability to release heat to space. There are three candidates.

So both through many lines of evidence, and also by applying some basic engineering understanding, the idea that increased GH gases are the primary cause of the warming the Earth has seen in the last ½ century or so seems very solid. No other explanation fits the evidence.

It seems my old Professors were right; its simple really when you get your system boundaries right. Watch the Dog, not just its Tail!

So when someone tells you that warming has stopped they are simply wrong. Probably spending too much time just looking at the Dog's Tail.

Glenn's post is excellent for it's clear-mindedness. It really highlights why the natural cycle idea, when addressed at the right scale, really is an instance of magical thinking, given the data we have in hand.

Great article that clearly explains the 'missing heat'. The only snag that I see is that it doesn't explain what causes the heat to be sucked down in to the deep (La Nina) or re-emitted (El Nino). Unless we can predict those, in theory, we could have La Ninas going on for decades, which will be a hard sell to the public when fighting the deniers. The other problem, of course, is that it's difficult to explain why heat in the ocean is caused by CO2 which is in the air.

Glenn,
couldn't it be argued that the huge time lag in deep ocean cycling could be responsible for temperature changes from decades or centuries ago?
In my experience the most sophisticated denier arguments attack the validity of graphs like the "ocean VS Land+ atmosphere +ice", by going into the details and asserting that there are major assumptions that are inaccurate. EG. arguing that ocean rifts are not adequately studied to determine Anthropocentric CO2 emissions. And I forget the actual argument, but something about how the CO13 to CO14 ratio is no proof of anthropocentric CO2 increase.
SO how much do we know about heat exchange for the entire oceans? Or do we not need to know that because we can determine the rate of change, and that is enough?

Guardianista2012 - "The only snag that I see is that it doesn't explain what causes the heat to be sucked down in to the deep"

Modeling in Meehl (2011) suggest mid-latitude oceanic gyres are sucking the heat down to the depths and that this predominantly occurs during La Nina-like periods. See SkS post: Ocean Heat Poised To Come Back And Haunt Us? Observations tentatively confirm this, but we'll have to see what the peer-reviewed literature has to say.

The other problem, of course, is that it's difficult to explain why heat in the ocean is caused by CO2 which is in the air

Yes, a common misunderstanding. Greenhouse gases, such as CO2, alter the thermal gradient in the 'cool skin' layer of the surface ocean. This causes the oceans to slowly accumulate heat over time. See SkS post: How Increasing Carbon Dioxide Heats The Ocean

And of course to add to Rob's point, why are the oceans still warming? If they were releasing heat to the atmosphere, they would show cooling, but they don't.

If the ocean ridges were producing most of the carbon increase (and necessarily overwhelming anthropogenic sources, the distribution of worldwide CO2 concentration would be rather different. But the observed pattern is one of highest concentrations in the NH and over land, thus disproving the ocean ridge hypothesis, which demands a pattern more akin to the global distribution of spreading ridges (I recall some nice animations of global CO2 distribution and the latitudinal pattern of increasing CO2 concentration but can't find them). High CO2 production in the SH by ocean ridges is not observed.

Two instances of 'loose' (lines 10 and 11) should be 'lose'.
One instance of 'new' in the fourth line of The Smoking Gun subsection should be 'knew'.
One instance of 'where' (fourth line from the end) should be 'were'.

Very good post, by the way, but you can delete this message for being related to a side-issue if necessary !

The hole is dismissing the Spencer no-heating measurement down 700 metres (altho it misses polar warm-current changes that have spiked in the 00s). It's more likely that the heat is in currents and layers that disappear in the measurement noise of a few thousand scattered buoy pins. It's similar to recent research finding CO2 levels in particular regions higher than the background 390ppm.

The bigger picture is an embarrassing sense of relief.

Yes, temperature rise is slowed to a crawl thanks to the oceanic pumping episodes. But if the region 1000 metres below the surface to 1000 metres above the surface isn't rapidly heating - and that's what counts - then technically-accurate butwaddabouts won't free one red cent for a response.

It could mean decades, even centuries, of repeated sequestering stalls; and that could slow or stutter the warming enough for adaptation to have a fighting chance.

And that's the relief: the world has collectively chosen to let GHG-pollution run amuk. If the deep ocean is the magic-sink that buys some time - thank gawd for it.

And as a footnote, the dictionary should be changed to allow looses to be a synonym for loses ... it actually reduce global internet traffic.

We live on a spherical rock with oceans of water and an atmosphere. Our only source of energy is the Sun. The recent period of an equilibrium of radiation from the Sun and the re-radiation back to space for the last thousands of years is where we adapted and flourished as a species.
The weather we see in our atmosphere is a very poor analogy for the similar chaotic currents in our oceans. The time constants for both systems are completely different. But they are very similar. Hence the unpredictability.
Us puny humans are trying to understand the changes we have made by our releasing or pollution of CO2 into our atmosphere.
By measuring the change in atmospheric temperatures we get an indication of the damage we are doing. The ocean temperatures seem to be lagging far behind but are far more sinister for long term equilibrium.
There is no doubt that greenhouse gases are the major driving forces that are the cause for the climate changes we are now seeing.
Looking at one tiny local phenomena will not negate the whole picture. Anyone who promotes this as evidence is a fool or a liar. Bert

The Oceans are a complex mix of forces. If we were dealing with a simple body of water heated from above convection would tend to push heat towards the surface but conduction, a much smaller factor would tend to push heat down. Then add that the oceans are salty and very deep and you can have salinity effects that counter the convection.

During the early 1980's I was involved in a project devloping Solar Ponds. Large deep pools of water that were heavily salted to produce stratified layers of differing density that could counter the circulation due to thermal buoyancy. The result was a pool that reached 80-90C at the bottom from solar energy from above - we had to put up safety fencing and warning signs. The project failed because we couldn't maintain the stability of the salinity gradient. But it showed clearly how salinity/density effects can counter thermal convective forces.

Then in the oceans add Coriolis Forces, the pumping effect of the Thermo-Haline circulation that drives the main ocean surface and bottom currents, and the shape of the sea floor and continents and you have a very complex system fo circulation patterns, that are certainly strong enough to overwhelm simple thermal convection towards the surface in some regions of the ocean, as shown in Meehl et al.

But this isn't uniform across the oceans. In other regions where currents & gyres don't operate, the ocean can be strongly stratified.

The most dramatic demonstration of this was during the 1950's, during the era of atomic testing. The USA tested a 'Depth Bomb', a nuclear Depth Charge - One explosion, guaranteed destruction of an enemy submarine. Several months after the test a research vessel returned to the area and took water samples, exploring how far the blast products had spread. They had horizontally over around 100 sq Kilometers. But the real surprise was vertical spread - to the best estimates they could make with the instruments they had, the blast products had only spread vertically in a laey 1 metre thick! After an nuclear blast, for stratification to re-establish so strongly shows how strong the forces driving vertical stratification are in the absence of other forces.

What all this tells us is that transfer of anything in the oceans - heat, dissolved gases etc is a complex mixture major flows alongs the oceans 'highways', and virtually no flow outside the 'highways'. If the highways change their behaviour then significant changes in heat storage patterns are entirely possible. And this is why the simple argument often used by skeptics that 'heated water rises!' is wrong.

"couldn't it be argued that the huge time lag in deep ocean cycling could be responsible for temperature changes from decades or centuries ago?"

Yes it could certainly be argued that if the total heat of the entire system wasn't rising. In a sense that is the basis of the whole 'we are recovering from the Little Ice Age' meme. If the atmosphere had cooled during the little Ice Age then the return of heat from the oceans would then explain surface warming. But the total system heat would not be increasing. And with the huge difference in heat capacity between the atmosphere and the oceans, it is hard to understand why such a 'recovery' is so slow. The extra heat that has shown up in the 0-2000 metre data in about 1/2 a decade is enough to warm the entire atmosphere by about 2 Deg C every year.

"EG. arguing that ocean rifts are not adequately studied to determine Anthropocentric CO2 emissions. And I forget the actual argument, but something about how the CO13 to CO14 ratio is no proof of anthropocentric CO2 increase."

There are two different arguments here. One suggests extra heat coming from ocean rifts etc. However total heat from within the Earth is only about 0.1 Watts/M^2 compared to the Forcing from a doubling of CO2 of 3.7 Watts/M^2. And it is incredibly hard to come up with a geological reason why the flux of geothermal heat would fluctuate on anything but geological time scales.

The other half of this is subsea sources of CO2, perhaps suggesting the rise in CO2 isn't due to us. There are a number of arguments against this. 1st. The C12/C13 argument is very simple. Natural carbon ratios are 99% C12/1% C13. The only places where this isn't true is anything derived from plants - since the photosynthesis mechanism used by most plants preferentially absorbs C12, anything plant derived is C13 depleted. So, Plants, Soils, Animals, and Fossil Fuels. So if the extra CO2 in the atmosphere is coming from subsea vents, it wouldn't be C13 depleted. So it wouldn't change CC12/C13 ratios in the atmosphere in the ways we have observed.
2nd, the subsea vent argument has to explain where the CO2 humanity has emitted has gone. And if our CO2 can be totally absorbed into 'something' why isn't the CO2 being similarly absorbed. The only plausible answer to that is that CO2 from the sea floor massively exceeds humanities cumulative emissions. 3rd. If so much is being released on the sea floor, how does it reach the surface? If it rises to the surface as bubbles, where is all this 'schwepervesence', where are the bubbles that no sailor has ever reported. If it is dissolving in the ocean then it must reach the surface via the ocean overturning circulation, which requires centuries. So what are the odds that centuries ago, before the start of the Industrial Revolution, venting on the sea floor started releasing huge amounts of CO2 that would arrive at the surface just in time to look like it was our emissions while our emissions have mysteriously vanished. And if it were dissolving down there in such quantities the Carbonate Chemistry & Ph of the deep waters would show characteristics of that. And they don't.

"SO how much do we know about heat exchange for the entire oceans? Or do we not need to know that because we can determine the rate of change, and that is enough?"

We don't know everything about heat exchange in the ocean, but we know a lot. We know how fast heat diffuses in still water. We have mapped the major ocean currents, including their speed and the volumes of water moving, we have mapped salinity distributions. And we have the ability to measure temperatures, and thus heat content in detail for half the oceans volume and to a much lower resolution for the other half.

As for what we need to know to know enough. Being able to measure heat content for the top half of the ocean and estimate whether the lower half s changing much is enough to do an energy balance. If the rate of total heat rise is continuing much as we expect we have a pretty good handle on what is happening. But more detailed studies such as Meehl help us understand more about the mechanisms.

Understanding Ocean warming is important to our projections of future warming. Less about how much the whole system will warm eventually, but more about the journey to that final state. Will it be a steady rise in surface temps, or alternating periods of high warming and hiatus. This all depends on how the oceans flip-flop about a little. But this doesn't effect much what the final result will be.

Yes, changes in ocean circulation might buy us time. However there is enough uncertainty around how circulation patterns might change in future that we can't count on that. So maybe it buys us time for adaptation. If adaptation is going to be enough, ultimately. Unfortunately it can also provide a pretext for slowing action to reduce CO2 emissions, leaving us more dependent on adaptation down the track. Personal view is that adaptation can only achieve adequate results if we are on a low warming trajectory. If we continue on the current high warming trajectory then the primary adaptation strategy we will use, willingly or otherwise, is mass, violent population decline.

And no adaptation strategy will slow the impacts of Ocean Acidification as CO2 climbs.

Personally I hope that the model results reported by Meehl are right and that this Hiatus ends soon. Only when we see more serious warming will the dam of Denial break. Humanity can alter our energy systems rapidly if we are sufficiently motivated. But that motivation is esentially an emergency war-time like mobilisation. We won't do that if most people can treat AGW as a problem to worry about later.

"it can also provide a pretext for slowing action to reduce CO2 emissions"
What 'slowing action'?? The global response to GHG-pollution is virtually dead. It's full-bore with the fossil fuels. 20 years after the danger was known, the response is on whimper.

"is mass, violent population decline."
Scare someone else with the Malthusian collapse - the inheritance will be Garbage Dump Earth.

"Mother Nature really hasn't done us any favours in the last decade."
Yes, it certainly has. And the reaction shouldn't be denial, it should be gratitude for the wiggle room - because so far that slowdown is the only activity on the road that hasn't been pedal-to-the-metal.

This ocean heating is all the result of down-welling long wave IR from the extra CO2 in the atmosphere? Imagine a 1 m2 section of equatorial ocean. What is the ratio between the amount of energy received by this patch from this down-welling long wave IR vs that received from direct sunlight over an average year? Do all 1 m2 patches of ocean, at any point on the globe, receive the same amount of down-welling long wave IR radiation? Is it stronger at the tropics than the polar regions? Thanks, in advance, for any answers.

I have to disagree. Physically Mother Nature might have given us some wriggle room. By Psychologically she has trumped us. Nothing is going to lull people into a sense, not of complacency, but of lethargy & inertia, more than the 'Nothing to Report Here' meme.

If Mother Nature (not wanting to over-anthropomorphise here) wanted us to act on this 'She' would have scared the living bejeesus out of is ages ago.

This is averaged out over the entire planet, rather than just the oceans.

So to your comment: "This ocean heating is all the result of down-welling long wave IR from the extra CO2 in the atmosphere"

Not quite true. Rather, the heating of everything, oceans, air etc is driven by changes in the balance of various factors. The previous temperature was based on the previous balance.When the balance changes, the temperature changes.

However, this varies hugely with latitude.

"Do all 1 m2 patches of ocean, at any point on the globe, receive the same amount of down-welling long wave IR radiation? Is it stronger at the tropics than the polar regions? Thanks, in advance, for any answers. "

Yes, this stuff varies hugely with latitude. In the Tropics the amount of incoming Solar absorbed is greater than that radiated to space. The difference in energy between the two is moved toward the Poles by the major circulation patterns of the weather systems.

So too the amount of downwelling radiation varies with latitude since this is driven by the temperarure profile of the atmosphere which varies with latitude.

Glen,
Really excellent clear informative exhaustive responses!
And I agree with you about Mother nature, though I will take a lag if nature will give it to us. I actually would hope for a significant increase in temps in the next few years to get the politics going and THEN a bit of a lag! I imagine that in 10 years we could really mobilize and make huge initial progress of transitioning away from fossil fuels, and 50 to really complete it.

Not sure I understand the question, but I'll have a stab and assume you're talking about why global warming, and particularly ocean warming, doesn't occur rapidly by human timescales. That's because the forcing by greenhouse gases grows gradually every year as we burn more fossil fuels. This is, however, obscured by natural variability in the climate system - El Nino/La Nina, the solar (sun spot) cycle for instance.

Woody @ 19 - CO2 is a well-mixed gas in the atmosphere. Therefore it's affect on the 'cool skin' layer of the ocean is global in scale, and more or less, uniform. And no, it is not stronger at the tropics than at the poles. That asymmetry is a function of the more intense heating that occurs at the equator, due to the more intense sunlight there.

A useful way of thinking about it, is similar to the way greenhouse gases work in the atmosphere - trapping heat and letting less escape to space. The same principle is at work in the ocean - greenhouse gases trap more heat in the ocean and less is able to escape to the atmosphere.

"If Mother Nature (not wanting to over-anthropomorphise here) wanted us to act on this 'She' would have scared the living bejeesus out of is ages ago."

Over-Gaia'd is exactly the way your response sounds. It isn't a supernatural entity. Your argument doesn't work with either the planet mechanics or the human reactions.

Tonydunc highlights the fallacy - you're seeking a 'significant increase in temps' on the absurd notion that it will wake up the world. Bad news - already had it (the 90s) and the world turtled on a response BEFORE the make-believe flatline.

You guys simply don't get it - the only slack and delay is natural buffering from the biosphere. The world had it's pro-active chance two decades ago. The collective decision voted for the 'good' pollution.

So check your 'I want a fire alarm' ego at the door, and start rooting for the biggest buffer possible - because tonydunc's if-then flunks on the 'then' and it only means more and bigger garbage dumps sooner.

Thanks Rob Painting, actually my question was, I can see how an ocean downwelling could momentarily draw warm water to the depths of the ocean, but convection should surely mean that the warm water would be drawn to the surface very quickly?

I've been giving this conundrum some thought. Could it be possible that the ENSO events are actually being caused by geothermal activity from below? We know the earth has a molten core, so you'd imagine the temperature rising from the core to the surface would fluctuate, and this could explain ENSO events better than heat being drawn down from above. That isn't to say that I'm suggesting that the earth's temperature is entirely dependent on geothermal activity, just that it's a combination of heat from the sun and heat from below. Heaven and hell, if you like.

Heat will only rise back towards the surface if the water below is warmer than that above. This will depend on how much mixing occurs when the warm water from the surface meets the cooler water at the bottom of the gyres. Just because the lower waters have been heated doesn't automatically mean that they will be warmer than the water above. The heat figures just mean that they are warmer than they had been previously.

Thanks Glen, I can see what you're saying there now. There's still a puzzle in my mind why the warm water would get drawn down in the first place, though.

Is there any problem with my suggestion that ENSO events could be sourced from below, though? We know there's heat down there, so why wouldn't it permeate to the sea floor and heat the water from below? Obviously, we're talking subtle temp changes but over a whole planet could explain the variable temps we see.

The point by #14 Glenn is interesting. Is there an educational web source which explains and if possible quantifies the different exchanges in the oceanic "energy system" (inside ocean, between layers, and also with atmosphere). For laymen, it is quite obscure: there's much attention for atmosphere mechanisms (3% of heat content) and few explanations for ocean (90%). For example, I don't figure clearly why an energy imbalance would imply just a heat content change in oceans. There are no other ways for dissipating energy?

Guardianista2012 -Is there any problem with my suggestion that ENSO events could be sourced from below, though?

Yes. ENSO is a tropically-driven phenomenon, is it your contention that these mysterious geothermal vents straddle the equator in the Pacific? Actually there are so many problems with your assertion that it's better you watch this animation and understand how ENSO operates, rather than put forth "what if......", and "maybe......"

There is a vast body of scientific literature on ENSO, and there was a recent (2012) review at NCAR which deals with the various proposed mechanisms - I'll see if I can track it down, if you're interested.

skept.fr - "For example, I don't figure clearly why an energy imbalance would imply just a heat content change in oceans. There are no other ways for dissipating energy?"

Increase the levels of greenhouse gases in the atmosphere and less heat escapes to space. The double-whammy is that greenhouse gases trap more heat in the ocean too. The combined effect is less heat being lost to space, and the Earth warms. This warming causes an energy imbalance at the top-of-the-atmosphere (less energy in the form of heat is radiated out to space). The current imbalance is, in effect, future warming in store for us.

The only way for the Earth climate to dissipate energy (if you correctly delineate the system boundaries, as Glenn Tamblyn has done in this post) is by radiating it to space. The heat content is the total of atmospheric, surface, ocean, and cryosphere segments, with the oceans representing by far the largest portion.

Increasing heat content in the oceans isn't dissipating a heat imbalance - it's simply going somewhere in the climate that's harder to directly observe/experience than the atmosphere. And that total imbalance is what is changing our climate over the long haul. That's the entire point of this thread!

Guardianista2012 - The amount of energy released by volcanic activity, and in fact by all heat percolating out of the Earth's core, is tiny with respect to the observed heat changes in the climate. Also note that modeling the physics of aperiodic circulations such as the ENSO shows such variations emerging from wind and circulation as we understand it - in other words, the physics of atmospheric and oceanic circulation show ENSO type variations as emergent properties of the system. No need for warming the bottom of the pot whatsoever.

Given the stratification shown in ocean temperatures, heat coming from the ocean floor or vents would be easily discernible as warm layers on the ocean floor. No such evidence exists to support your hypothesis.

So: there's insufficient energy available from geothermal activity, and no evidence for vents driving circulatory changes.

Guardianista2012- "I don't think my suggestion should be dismissed out of hand"

Why not? There have been decades of research on this topic. Has it not occurred to you that this may have been seriously considered decades ago and found wanting? It simply does not gel with the observations. I suggest you watch that animation to gain a better understanding of ENSO.

And for your information, the tiny contribution of geothermal heat in the very deep sea, the abyssal ocean, is responsible for the upwelling arm of the Thermohaline Circulation. It's not exactly like scientists don't know this.

I read this line: But the absolute clincher is that the amount of heat going into the oceans is so great that no other source of heat here on Earth could supply it and was curious to know the numbers. While I had an intuitive sense the statement was correct, having studied geothermal heat as a power source in the past, I felt interested to see just how different the heat fluxes from above and below are, just in case I ever get asked.

Now obviously I'm comparing apples and oranges to an extent, there isn't much mixing between the parts of the ocean where these heat flows wind up, but the numbers are interesting nonetheless. The heat flow into the top 700 m from 1993-2003 averages out at 257 TW (from the IPCC report graph), while the geothermal heat flow from oceanic crust is 35 TW (from Pollack, 1993; heatflow of 97 mW/m2). So the geothermal flow is only ~13% that of the additional heat being pumped into the top 700 m, which is quite a small amount.

In fact I'm a little surprised that no-one I've ever talked to has asked whether the OHC anomaly could be coming from the bottom up instead. Of course, for this to be the case, the oceans would have to operate on a vastly different mechanism to how they are known to operate, even if the heatflow was sufficient.

To emphasize KRs point, one need only look at the fact that temperature within tens of meters away from those vents is back to 3-4C. The vastness of the deep ocean provides enough heat capacity to easily dilute that geothermal heat and maintain a very constant temperature. For those geothermal vents to force upwelling through the permanent thermocline, they would have to exert a wide ranging and persistent effect of temperature that would be very obvious. We simply do not see that.

wrt to Geothermal Energy, the following from Wikipedia gives some sense of its relative magnitude:

"The Earth's internal thermal energy flows to the surface by conduction at a rate of 44.2 terawatts (TW),[33] and is replenished by radioactive decay of minerals at a rate of 30 TW.[34] These power rates are more than double humanity’s current energy consumption from all primary sources, but most of this energy flow is not recoverable. In addition to the internal heat flows, the top layer of the surface to a depth of 10 meters (33 ft) is heated by solar energy during the summer, and releases that energy and cools during the winter.

Outside of the seasonal variations, the geothermal gradient of temperatures through the crust is 25–30 °C (45–54 °F) per kilometer of depth in most of the world. The conductive heat flux averages 0.1 MW/km2. These values are much higher near tectonic plate boundaries where the crust is thinner. They may be further augmented by fluid circulation, either through magma conduits, hot springs, hydrothermal circulation or a combination of these."

0.1 MW/km2 is 0.1W/M2. Contrast this with Solar absorbed by the surface at around 161 W/M2, back radiation at around 333 W/M2 and the forcing due to a doubling of CO2 of 3.7 W/M2.

Geothermal is present but it is 3 orders of magnitude smaller than the main components of the energy balance in the atmosphere.

And while it is conceivable that a major subsea volcano might put out enough heat to cause a circulation, heat flows from diffuse sources like vents are pretty unlikely to to contribute much. And the key issue with Geothermal energy is that, apart from major eruptions, there is no sensible mechanism for why the output wouldfluctuate significantly.

What must also be remembered is that when we look at the major ocean currents, they may move slowly but the water volumes are massive. So there is a huge amount of kinetic energy in them that can then drive all sorts of complex circulation behaviour. So secondary circulations like gyres aren't really surprising in the context of the whole ocean, and that their behaviour can change from time to time isn't really surprising either.

Matt Arkell. The important issue with the geothermal flow is not just its magnitude which is part of the normal energy balance of the planet, but how much that flux could change because it is that that would be the driver of any contribution it might make to change in the ocean heat content.

And another point about the estimation of geothermal energy... the petroleum industry invest heavily in understanding this. It is a crucial input to sedimentary models used for determining if and when a basin could be generating oil and gas. I think they would have noticed and reported loudly if there was any suggestion that the accepted geothermal heat flux rate were underestimated. Volcanoes and associated events are extremely localised heating.

I can't claim that this article proves my guess was right, but it does encourage me to believe the guess I made a couple of years ago: if there is a successful "geo-engineering" project to save the world from the worst of AGW, it will be accomplished not by spraying aerosols in the air, but by manipulating ocean currents so that the oceans can absorb more of the heat.

That said, I still believe that we do not know enough to embark on ANY geo-engineering project yet, we might not know enough for decades to come. We could easily end up just making things worse.

Glenn Tamblyn: The important issue with the geothermal flow is not just its magnitude which is part of the normal energy balance of the planet, but how much that flux could change because it is that that would be the driver of any contribution it might make to change in the ocean heat content.

I'm aware of that, however I wanted to get a handle on the magnitude of the difference between the two. If the heat flux (averaged across the entire ocean floor) is ~13% of the total change in heat content, then the changes required in geothermal heat flux would have to be enormous in relation to the average value.

While searching for data, I found this page showing the variation across the ocean floor in the geothermal heat flow data. The greatest values are along the East Pacific Rise, and reach no more than ~350 mW/m2. This suggests that enough variability doesn't exist, certainly not on the scales necessary to have a significant impact on OHC worldwide.

I’m pleased to see such knowledgeable people posting. Thanks. The comments help me so much to increase my knowledge and understanding.

Might I add, has anyone observed any published results on the measurement of the strength and northern boundaries of the Atlantic Current or the Gulf stream? I understand that it is known by several names. The last I can find was in 2005.

34 (Rob), 35 (KR) : for example, I don't understand very clearly what energy is concerned in this D'Araso et al 2011 paper. By "dissipation" rather than "storage", that is the kind of phenomena I've in mind (not just this one in particular, but the nature of energy in the ocean system). For example, once LW from CO2 (or SW from the Sun) warm the upper layers by radiative transfer, what will happen exactly in the ocean? How this oceanic heat surplus is transferred (where, when, which rate, which quantity, etc.)? Can heat fuels work, like in a Carnot cycle, or can a thermal energy produces be transformed in a kinetic energy? My questions are very basic and naïve, and that's why I search an educational introduction to ocean as an energy system.

The 0-2000m OHC chart shows a rise in OHC from roughly 12E22 Joules to 15E22 Joules over a period of 2005-2011 - 7 years.

This is a rate of 3E22 Joules over 7 years or 0.43E22 Joules/year = 43E20 Joules/year. 145E20 Joules/year equates to a TOA imbalance of 0.9W/sq.m. So the 0-2000m OHC increase equates to 0.27W/sq.m at TOA.

2000m to the bottom is very uncertain. The last number I recall was around 0.1W/sq.m (Willis?)

This makes a total OHC increase around 0.37W/sq.m TOA equivalent which is far short of the modelled 0.9-1.0W/sq.m - 10 year hiatus notwithstanding.

What are you claiming is the OHC increase measured from 2000m to the bottom?